RGB CMYK issue, missing functionnality in Photoshop?
d303 (14 points) | Fri, 2010-01-29 20:58Hi everyone!
I am having a little bit of an issue with the famous RGB/CMYK conversion!
In my case, I have been given a CMYK ICC color profile by the printer. So all I did was to convert all my RGB pictures to CMYK and embed them with the CMYK profile with an action droplet.
So far, all is good.
So far color photographs, no problem.
The issue is with the blacks when working in Indesign.
Small text is C0 M0 Y0 K100.
For larger black title, the printer recommends using a RICH black, C60 M40 Y40 K100. Which is easily set within Indesign for large objects, titles or for black backgrounds.
But I have also some black & white logos for which the black RGB was R0 G0 B0. That RGB image comes from a large size indexed colour picture, and by being converted as RGB, it went from having only 2 colors (b&w) to having b&w and various shades of grey on the edge between b&w. And I would like my black to be a rich black C60 M40 Y40 K100 in Indesign.
But the CMYK ICC profile provided by the printer gives it a black which is C82 M74 Y49 K95 under photoshop, and it remains the same under Indesign as a result.
So now the question:
When converting from RGB to CMYK with the ICC profile, is there a way for me to then select the main black color (which used to be R0 G0 B0 and is now C82 M74 Y49 K95) and change it's CMYK value to the one I desire so that the whole image changes as well (meaning white, then the rich black I need C60 M40 Y40 K100 and then the various shades of grey would adjust themselves too according to the change I made to that rich black!).
I have tried many things, including playing with the channel mixer etc. but it doesn't make me pick the black and changed it's CMYK value so that all the rest of the image changes also accordingly.
Is there a way to automatically convert that black to the rich black percentages that I need with the rest of the image changing accordingly?
Thanks for reading, hoping someone will have an idea of what I can do?
When converting from RGB to CMYK ....is there a way to select the main black color.....and change it's CMYK value to the one I desire
Sorry. Nope. You have to mask it.
All blacks in RGB will convert to Rick Black in CMYK. It can't work any other way.
Whoa. Wait a minute. The ICC Profile your printer gave you turns R0 G0 B0 into CMYK C82 M74 Y49 K95. That would be VERY unusual for Yellow to be so low. While the TAC value is just fine for Web press (82+74+49+95 = 300TAC), I'd still give your printer a call and mention these values to them.
They are using an HP Indigo, a digital offset printing press. And provided a CMYK profile optimized for the HP Indigo presses (HP5000SemimatteExp05.icc). So I don't think there is anything wrong with the yellow being slightly lower. Some people only use C100 M0 Y0 K100 for their rich black etc. question of preference. But I am being told I should use C60 M40 Y40 K100 which is not what the ICC profile converted the R0 G0 B0 black into... hence my request for a solution?
Ahhh! OK then. I think I can help.
The rich black of 60,40,40,100 and the black generated by the ICC Profile are two different beasts.
If you have a logo, very large block type or large areas of flat black, you would use the recommended 60,40,40,100 by manually entering the CMYK value in Illustrator or InDesign. The ICC profile, on the other hand, is used for creating CMYK separations of RGB photography in Photoshop. It should have a different black value. This is completely normal.
So, in short. If your RGB files are photographic in nature, it's fine. Don't touch a thing. If, on the other hand they are logos, then I'd recreate them as vector OR create a mask to select them and bring them down to the 60,40,40,100.
Honestly, since this is a digital press (toner based, I assume) then this shouldn't be an issue at all and I'd use the ICC max black. But hey, whatever the printer says. Its just CYA really.
BTW, it's easy to create a mask of a black & white logo in RGB. See about using channels to create selections and Alpha Channels. In short, you already have a perfect mask in RGB mode using any of the RGB channels. Dupe one of the channels into a new alpha, convert to CMYK, make the alpha channel a selection and fill in with desired CMYK vals.
Not very clear. Once I duplicate one of the 3 RGB channel and then convert the whole thing into CMYK, I have 5 channels (all CMYK, the C, M, Y & K) plus the duplicated one. But how do you get to change the tint of the duplicated one to the desired C60 M40 Y40 K100? The Colour slider becomes disabled (all slider in the colour palet menu are disabled, only slider spectrum are enabled), and doesn't show the 4 CMYK slider, probably due to the fact that the channels are not only CMYK anymore as there is the use of a 5th channel. And again, the same problem remains, there doesn't seem to be a way to change the CMYK % of a color (and have all the other colours affected), nor does there seem to be an option to change the colour of one channel to a specific CMYK colour.
If I just convert the RGB file into ICC CMYK profile, and then just create a new layer based on a selection from the black channel in the CMYK channels, and then fill it with desired CMYK colour, it even gets worse, it create the object in a black transparent colour, even though the option is set as "normal" in the layer setting menu. It's driving me mad :(
Ok, I tried again. And it worked with 2 pictures. Don't really know what was the difference (closed photoshop and reponed...).
So from my Black & white RGB file, I created a new layer first. Then used the CMYK ICC profile to convert the image. Then I went into the channels, then cmd + clicked on one channel, which created a temporary selection of the surrounding of the black shape. Then inverted the selection so the black shape is selected, then came back on my new top layer and filled it with the desired CMYK color (shift+F5).
And since the selection was based on one CMYK layer, the variations of greys on the edge of the black shape were taken into consideration by the program in accordance with the CMYK value I chose! Hooray!
Now I have my B&W TIF file with the right color profile, in CMYK, and the right rich black! Ready to place in indesign...
Thanks caoimghgin!
But I have also some black & white logos for which the black RGB was R0 G0 B0. That RGB image comes from a large size indexed colour picture, and by being converted as RGB, it went from having only 2 colors (b&w) to having b&w and various shades of grey on the edge between b&w. And I would like my black to be a rich black C60 M40 Y40 K100 in Indesign.
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Huh, I think you are doing things the hard way? If I understand you correctly, converting BW logo to rich black...the easiest way is to simply convert b/w logos into bitmap images then you can apply the rich black swatch within Indesign. But why would b/w logos be in rich black?